1. Field of the Invention
The present invention relates generally to data transmission, and more particularly to packet switching between various devices within a network.
2. Description of the Prior Art
With early networked storage systems, files are made available to the network by attaching storage devices to a server, which is sometimes referred to as Direct Attached Storage (DAS). In such a configuration, the server controls and “owns” all of the data on its attached storage devices. A shortcoming of a DAS system is that when the server is off-line or not functioning properly, its storage capability and its associated files are unavailable.
At least the aforementioned shortcoming in DAS systems led to Network Attached Storage (NAS) technology and associated systems, in which the storage devices and their associated NAS server are configured on the “front-end” network between an end user and the DAS servers. Thus, the storage availability is independent of a particular DAS server availability and the storage is available whenever the network is on-line and functioning properly. A NAS system typically shares the Local Area Network (LAN) bandwidth, therefore a disadvantage of a NAS system is the increased network traffic and potential bottlenecks surrounding the NAS server and storage devices.
At least the aforementioned shortcoming in NAS systems led to Storage Area Networking (SAN) technology and associated systems. In SAN systems, storage devices are typically connected to the DAS servers through a separate “back-end” network switch fabric (i.e., the combination of switching hardware and software that control the switching paths).
With the deployment of prior SAN technologies in the growing enterprise-class computing and storage environment, several challenges are recognized which have no solutions prior to the present invention. One such challenge is to provide a scalable system wherein thousands of storage devices can be interconnected. One existing solution is to cascade together a multitude (tens to hundreds) of small SAN switches, which results in scenarios where a multitude of hops are required to reach a destination. Performance (e.g., latency and bandwidth) and reliability suffer in such an existing solution. Additionally, a configuration that includes hundreds of interconnected switches is also inherently difficult to manage and to diagnose faults therein, both from a hardware and software perspective. Still further, since no available SAN protocol is truly ubiquitous enough to be readily integrated with other networking architectures in a heterogeneous SAN environment, bridges and conversion equipment are needed, which increases the cost and management of such a system.
FIG. 1 shows a block diagram of a Storage Area Network 100 of the prior art connected to a client 110 through an Internet 112. The SAN 100 includes an IP router 114, an IP switch 116, a plurality of servers 118, 120, 122, and different storage media represented as Redundant Arrays of Inexpensive Disks (RAID) 126, Just a Bunch of Disks (JBOD) 128, 130, and tape back-up 132, connected to the separate “back-end” network switch fabric 134 described above.
The network switch fabric 134 includes one or more base racks (not shown) capable of switching signals. Each base rack includes a number of ports such that a signal received into one port can be directed to an appropriate destination port coupled to a destination component such as a server 118 or a RAID 126. Base racks ideally include a large numbers of ports to be able to simultaneously switch multiple signals amongst multiple components, however, 8 and 16 port base racks are most common. Multiple base racks can be used to form a network switch fabric 134 to provide redundancy, to increase switching capacity, or to accommodate more components than can be handled by a single base rack.
FIG. 2 illustrates how two base racks 200, 201 of the prior art can be cascaded together as part of a network switch fabric 134. Base racks 200, 201 each include a plurality of line cards 202, each including a plurality of ports. Each line card 202 is connected through a backplane 203 to a switch card 204. Some of the ports on the first base rack 200 are connected to ports on second base rack 201 by connectors 205, of which only one is shown for simplicity. Accordingly, even though the two base racks 200, 201 together may include 32 ports, since some ports are dedicated to connecting the two base racks together the number of ports available as input and destination ports is correspondingly reduced.
In some instances, a packet received into a port of first base rack 201 may be addressed to a component that is not directly connected to a port of base rack 201, and therefore would need to be switched to another base rack having such a port connection. Accordingly, FIG. 2 also illustrates how a packet introduced into a port of the first base rack 200 would be routed to a port on the second base rack 201. After ingress, for example through port 0 coupled to a line card #0 202, the packet passes through the backplane 203 to a switch card 204. Switch card 204 sends the packet back through the backplane 203 and through line card #1 202 to another port, here port 15, that is dedicated to communicating with the second base rack 201. The packet then travels over connector 205 and enters second base rack 201 at another port, here port 23. Lastly, the packet is sent from a third line card #0 202 in second base rack 201 to a second switch card 204 and finally to a fourth line card #1 202 from which it emerges through the appropriate port. It will be appreciated that a modern SAN 100 may comprise hundreds to thousands of transmission lines, and accordingly, to switch a packet between any two of these transmission lines requires cascading together potentially hundreds of base racks 200 in the manner shown.
It will be appreciated that not only is the number of useful ports reduced by cascading in such a fashion, but a packet that must be switched through more than one base rack 200 will traverse two additional line cards 202 for each additional base rack 201 it must pass through. Accordingly, what is desired is a faster and more efficient switching device with a greater proportion of useful ports.